Rotary selector switch construction with rotor interlocking means



Aug- 10, 1955 E. J. MASTNEY 3,200,208

ROTARY SELECTOR SWITCH CONSTRUCTION WITH RoToR INTERLOGKING MEANS Filed July 2, 1962 6 Sheets-Sheet l Aug. 10, 1965 E. J. MAs'rNEY 3,200,208

ROTARY SELECTOR SWITCH CONSTRUCTION WITH ROTOR INTERLOCKING MEANS 6 Sheets-Sheet 2- F'iled July 2; 1962 I" ugflO, 1965 E. J. MAsTNEYv 3,200,208

ROTARY SELECTOR SWITCH CONSTRUCTION WITH ROTOR INTERLOCKING MEANS Filed July 2, 1962 6 Sheets-Shea?l 3 ROTARY SE ECTOR SWITCH CONSTRUCTION WITH ROTOR INTERLOCKING MEANS 6 Sheets-Sheet 4 Filed July 2, 1962 mm @WWW Wm. NN NQ NN QQ N@ @www afm?

Aug. 10, 1965 E. J. MAsTNEY C 3,200,203

ROTARY SELECTOR SWITCH CONSTRUCTION WITH ROTOR INTERLOCKING MEANS Filed July 2, 1962 6 Sheets-Sheet 5 Aug. 10, 1965 E. J. MASTNEY 3,200,208

ROTARY SELECTOR SWITCH CONSTRUCTION WITH ROTOR INTERLOCKING MEANS Filed July 2 1962 3,20tl,2tl3 ROTARY SELECTGR SWITCH CONSTRUCTIN WITH RGTOR INTERLOCKING MEANS Edward l. Mastney, Hinsdale, Ill., assiguor to Oak Manufacturing Co., a corporation of Delaware Filed `Iuly 2, 1962, Ser. No. 206,862 21 Claims. (Cl. 20tl 6) This invention relates to an electrical switch, and, more particularly, to a rotating miniature switch adapted to be assembled in multiple sections.

It is an object of this invention to provide an improved switch.

It is a further object of this invention to provide a switch of a construction which is readily sealed against effects of changing atmospheric conditions such as humidity.

It is still a further object of this invention to provide a W-cost switch that is readily assembled into a plurality of ganged sections for switching externally connected electrical circuits.

Accordingly, it is one feature of this invention to provide a rotary switch comprising a housing, a body portion, including a stator having electrical contacts, held in the housing, a rotatable member having a contact arm extending through the housing into body portion, and means in said rotatable member for positioning the body portion with respect to the rotatable member in a fixed spatial relationship wherein the Contact arm is held in rotatable contact with the electrical contacts.

Y It is a further feature of this invention to provide a switch wherein there is provided a rotor, a driving shaft, and a stator held in fixed spatial relationship with said rotor and wherein is provided a slidable coupling between the rotor and the shaft to provide proper seating of a contact arm held by the rotor with the stator.

It is yet a further feature of the invention to provide a rotor having a plurality of projections having an annular groove formed thereabout for engaging with a stator, which flex inwardly to allow seating of the rotor in the annular recess.

Still another feature of the invention is to provide a multiple section switch having a shaft, a plurality of rotors couplable to each other in a series relationship, one of said rotors couplable to the shaft and a plurality of stators individually held in individual recesses in the rotors wherein the coupling between shaft and stator allows for slidable longitudinal motion to provide proper contact between individual contact arms held in said rotors with respective stators.

Further features and advantages of the invention will become apparent from the description of the following drawings, wherein like parts have Ilike reference numerals and wherein:

FIGURE 1 is a perspective view of the switch embodying the invention;

FIGURE 2 is a switch similar to FIGURE 1 with portions ofthe cover broken away;

FIGURE 3 is a sectional view along lines 3 3 of FIGURE 2;

FIGURE 4 is a sectional View along lines 4 4 of FIGURE 3;

FIGURE 5 is a sectional view along lines 5 5 in FIGURE 3;

FIGURE 6 is a sectional view along lines 6 6 of FIGURE 2;

FIGURE 7 is a sectional view along lines 7 7 in FIGURE 2;

FIGURE 8 is a sectional view along lines 8 8 in FIGURE 3;

FIGURE 9 is a sectional view along lines 9 9 in FIGURE 3;

FIGURE 10 is a sectional view along lines 1tl 10 in FIGURE 3;

FIGURES l1 and 12 together comprise an exploded View of the switch;

FIGURES 13 through 17 are alternate views of the reverse sides of individual items shown in FIGURES 1l and 12; and

FIGURE 18 is a sectional View of a second embodiment of the invention.

Referring now to FIGURES 1l through 17, which show an exploded view of the switch and include detailed views of the elements thereof, the switch may best be understood by dividing it into three portions, the housing, the shaft and rotor, and the stator portion.

The housing includes a bushing 20, a front cover 21 and a rear cover 22. The bushing, generally cylindrical in shape, includes a threaded portion 23 and a portion of enlarged diameter 24, including a pair of keyways 25, 26 and an annular section 27 having an outer portion slightly larger than the shank portion. A cylindrical aperture 28, generally coaxial with the bushing 2li, receives a shaft through the bushing. In addition, there is a stop pin 29 having its axis generally parallel to the axis of the cylindrical aperture and extending into the housing when the bushing 2i) is mounted on the front cover 2l.

The front cover 21 is generally square in cross section and has a circular aperture 3l slightly smaller than the outer rim of the annular portion 27 which receives aperture 31 and holds it in a sealed relationship. In addition, a pair of keys 32, 33 are adapted to engage the keyways 25 and 26 on the bushing. The end of the front cover opposite the aperture 31 is formed with a tapered portion 34. The rear cover 22 has a tapered recess 35 corresponding in configuration to the tapered portion 34 of the frontcover which it receives in a sealed relationship. The rear cover has a rectangular cross section similar to that of the front cover, and when the switch is assembled, the entire housing is substantially sealed against varying air and humidity conditions. The rear cover also includes a plurality of wire-receiving nipples 36 and allows a plurality of wires 37 to pass therethrough for connecting to electrical circuits to be switched. The length of the rear cover 22 varies depending upon the number of switch sections to be incorporated in the switch, and FIGURE 1S shows a switch including three such sections.

The rotating portion of the switch includes a shaft 4i), clamping ring 4l., rotor 42, a contact spring 43, and a rotor plug 44. In the embodiment of the invention shown in FIGURE 18, a plurality of rotor members and contact springs are shown. Such structure will be discussed hereinafter.

Shaft 40, in this instance composed of stainless steel, has an annular recess 45 formed therein for receiving clamping ring 4I when shaft 4@ is in place in the cylindrical aperture 28 of bushing 20. This serves to maintain the shaft against la longitudinal motion but allows it to be rotated about its ams. A portion 46 of the shaft 40, having a larger diameter than the rest of the shaft, has a recess t7 formed therein for engaging with stop pin 29 under certain operating conditions to be hereinafter discussed. In addition, portion 46 has a cylindrical aperture d formed therethrough for receiving an index spring 49 and a pair of index balls 50, 51. A series yof projections 52 extending longitudinally from the portion 46 ydefine a pair of mutually perpendicular slots 53, 54 whose axes intersect with the axis of the shaft.

Rotor 42, of an insulating material, has a pair of ridges 60, 6I formed on one face of the rotor mutually perpendicular and extending longitudinally from the rotor 42. On the face of rality of substantially planar faces 92.

,E f the rotor oppositeV ridges dii, 61 are a plurality of tapered projections 63 extending longitudinally from the rotor and dening a pair of mutually perpendicular Yslots 6d, 65 which extend into the rotor 42 and provide for receiving the contact spring 43. In addition, a slot 66 extending circumterentially around the tapered projections; e3 is provided for maintaining pressure on the contact spring as hereinatter discussed.

Ridgeyiii having a flaring end portion has a width dimensiony slightly larger than the slot width 53 on shaft itl andprovidcs a frictional lit therewith when the rotor and Y shaft are assembled'and allows some longitudinal motion 55 in rotor t2 and providesvslidable frictional couplingV when the rotor plug is assembled in the rotor. Y

A sealing ring 'f2 provides a seal between shaft di) and front cover 21 when the shaft is assembled in the bushing ,20 and provides for sealing the entire housing.

The inner stationary portion of the switch includes an index plate dit, a front spacer 31, a stator 82, and a rear spacer 83. FIGURE showsV the stator S2 to include a plurality of arcuate electrical contacts 85 formed about an aperture S6. A series oftabs 8'7 extend from the contacts and provide connections to a plurality of wires 37. The arcuately ar-ranged contacts are selected so that certain switching functions may be performed in electrical circuits connected to the wires 37. The arrangernent is determined by the specific switching functions desired. When assembled, stator 82 tits into the annular recess 66 on rotor 42 providing contact pressure between Contact spring 43 and the arcuate-electrical contacts 8S. The tapered longitudinally extending members 63 provide for' such assembly compressing as the s'tatoris pushed towards the rotor and spring back after the annular aperture Sdis'positioned within the slot 66. y Rear spacer S3 has a series of slots 9d extending longitudinally'about its peripherythat allow wires S'therethrough and Vpermits the wires to pass through nipples 36.

Front spacer 81 is provided to properly position index plate St'with respect to the portion 46 of shaft 4i?.

Plate Sti of stainless steel has an aperture formed therein having a plurality of index recesses 91 and a plu- The index plate Sii, front and rear spacers 8i, 83 and stator 82 are held in lixed relationship by a spring washer 94 and a pair of spring wires 9S, 96. Slots in the front and rear spacer, stator, andindex plate are provided for the wires. i When the shaft is rotated, Vthe balls Sii, 51 are moved `from one detent recess 91 along a planar surface 92 to the next recess 91. At the same time, the contact spring is rotated bythe rotor d2 and contact is madebetween different arcuate electrical contacts on the stator 52. Thus, the switching of external circuits is performed.

FiGURE l is a view'of 'an assembled switch constructed in accordance withthe invention and includes bushing 2i), yfront. cover 21 yandV rear `cover 22. The dashed line por- 'of FIGURE 2, shows the assembly of a single section switch. In this View, the shaft is in substantially the same position as shown in the exploded views of FGURES 11 andr 12. Contact'garrn 43 is shownvcont'acting arcuate contacts on stator 52 completing the electrical circuits between a pair of wires 37. i

v- FIGURE 4, a Vsectional view along lines 4 4 of FIG- URE 3, shows balls Si), S1 under the urging of index spring asesinos a' Y l i9 engaging detent or index portions 9i of the index plate Sii and the dashed lines show a second position of the shaft and balls.

FiGURE 5, a detailed sectional view along lines 5 5 of FIGURE 3, shows a portion of contact spring member 43 contacting. arcuate contact sections 35 and completing the Velectrical circuit between a pair of wires 37. The dashed lines show a second positionof the contact spring member 43 when the shaft has been rotated to a second position.

FiGURE 6 is a partial cross-sectional view along lines 6 6 in VFiGURE 2 with the shaft in the position indicated in the exploded View of FiGURES l1 and' 12. Pin 22 is shown in the recess section d'7 of shaft Kitt. n Ridgemember di? is shown in the slot defined by projections 52 ofthe rotor 'and is in slidable mechanical contact therewith.

The locking arrangement between the taperedprojection 63 of rotor 42 and the ridge section 7i) of rotor plug 44 is illustrated. Stator 82 is shown confined within the recess portions 66 of rotor 42.

FIGURE 7, a partial cross-sectionalv view along lines 7 7 of FGURE 2, wherein the shaft is partially rotated from the position shown in FGURES ll and 12, further illustrates the lmating between the shaft, rotor, and rotor plug. v

FGURE 8, a sectional view along lines 8 8 in FIG- URE 3, illustrates the relationship between pin 29 and the recess portion 4'7 on shaft 49. In this view, `the shaft has been rotated 60 from the position shown in FIGURES l1 and 12,.

FGURE 9, a sectional view along lines 9 9 in FIG- URE 3, shows the spring washer 94 in position and held l therein by the wires 95, 96.

FIGURE l0, a sectional view along lines M ti in FGURE 2, shows the wires 95, 9d in position to hold the index number, front spacer, stator, and rear spacer in a fixed relationship. In this igure, the shaft d@ has been rotated from the posit-ion shown in FIGURE 3.

FIGURE 18 is a partial cross-sectional view of a switch having three switch sections ganged tor operation lfrom .a common shaft. In this ligure, parts similar to Vparts discus-sed in the previous iigure carry similar refer- Y section. Such length is determined by the number of sections to be ganged.

tion itil represents possible extensions of the switch when f The rotating portion of the switch includes shaft 49 driving a plurality of rotors 412 and having a rotor plug 44. As previously discussed, the ridge members 60, di provide the direct coupling between rotors Vand between the first rotor and the longitudinal projections-52 on shaft dit. 2

An index plate Sti and a front, spacer Si are provided as before, and, in addition, there Yare two additional spacers M4 and H5 anda rear spacer d2. A spring Y washer 94 similar to the previous spring washer is held against the rear spacer 83 by a wire 115 of sutiic-ient V,length to extend through recesses'in the spacers and to clamp the index plate Sti and the spacers ina lixed physical position with respect to each other. A second wire similar to wire M6 is provided (but not shown). As before,.individual stators 82 are confined within recesses in respective rotors and electrical contact is maintained between the arcuate contacts on the stators and the contact arms. Wire 12) is shown electrically connected to an arcuate contact on the lettward stator, wire 121 con-l nected to the middle stator and wireA 122 connected t0 the rightwardly positioned stator. Additional wires 123 and Haare shown extending from the rear cover but are not' shown connected toany ofthe stators for the sake that they would lmake of clarity, itV being understood electrical contact within the switcl Assembly of the switch as shown in the first `seventeen figures is as follows. Bushing 2.0 is mounted to front cover 21 and pin 29 is inserted in the bushing. A rotor is then inserted in the slots 52 on shaft 40, a contact spring placed in the slots 64, 65 of the rotor and the stator, having wires soldered to respective ones of the arcuate contacts, is forced over the tapered members of rotor 42 and seats itself in the recess 66 of the rotor. Then, rotor plug 44 has its projections 70, 71 fitted into the respective slots on rotor 42 with which it locks. The rear spacer and the spring washer, having wires 95, 96, are then placed adjacent the stator, and the entire shaft and spacer assembly is placed in the rear cover with the wires from the stator extending to nipples 36. A front spacer 81 is then placed adjacent the stator and the index plate assembled next to the front spacer with the wires 95, 96 then clamped into position. Index spring 49 and balls 50 and 51 are placed in the cylindrical aperture 48 prior to the assembly of the index plate. A sealing ring is placed upon shaft 40 and the entire assembly tted together with the front cover and bushing and held in place by clamping ring 41.

FIGURE 3, among others, clearly illustrates the sliding frictional coupling between the shaft 40 and rotor 42. As can be seen in this ligure, shaft 40 is xedly held against longitudinal motion in the bushing 20 by clamping ring 41 and the sealing ring '72 butting against the shaft. In a like manner, the index plate 80, front spacer 81, stator 82, and rear space 83 are coupled in fixed relationship by the spring washer 94 and wires 95, 96. The wires 37, extending through nipples 36 and making contact wi-th arcuate contacts on stator 82, are in a like manner fixedly held within the nipples. Therefore, the rotor 42 positions itself with lrespect to stator 82, and the projections 60, 61 on rotor 42 slide with respect to the projections 52 on shaft 40 to allow for this seating.

In alike manner, as shown in FIGURE 18, wherein a plurality of rotors and stators are coupled and driven by a shaft 40, slidable motion along the longitudinal axis of the switch is provided by the respective projections on the rotors and the shaft.

In one embodiment of the switch, the actual dimensions of some of the component parts are as follows:

Shaft 40-Length l.564,'diameter of portion 46, .240"

Rotor t2-Axial length .212", depth of slot 64, 65, .134", major diameter of projection 63, .171", diameter of slot 66, .150

Stator 82-Width and height .350, aperture 46 diameter .156

Index plate Sti-Front spacer 81, rear spacer S3, width and height .350" Front cover S14- Outer dimension .400 sq., inner dimension .356 sq., length .200

Rear cover 22--Outer dimension .400" sq., inner dimension .356 sq., length .261 Bushing 20*Overall length I claim:

1. A rotary switch comprising: a housing; a body portion, including a stator having electrical contacts, held in said housing; a rotatable member, having a contact arm, extending through said housing into said body prtion; means associated with said rotatable member for positioning said body portion with respect to said rotatable member in a iixed spatial relationship wherein said contact arm is held in rotatable contact with said electrical contacts; a shaft extending into said housing; and means coupling said rotatable member to said shaft for rotation therewith and for limited longitudinal movement with respect thereto.

2. A rotary switch comprising: a housing; a body portion, including a stator having electrical contacts and an index plate, held in said housing; a rotatable member, having a contact arm and indexing meansJ extending through said housing into said body portion; means associated with said rotatable member for positioning said body portion with respect to said rotatable member in a fixed spatial relationship wherein said contact arm is held in rotatable contact with said electrical contacts and wherein said indexing means is confined within said index plate; a shaft extending into said housing; and means coupling said rotatable member to said shaft for rotation therewith and for limited longitudinal movement with respect thereto.

3. A rotary switch comprising: a housing including a stop means; a body portion, including a stator having electrical contacts, held in said housing; a rotatable member, having a contact arm and a recess operably associated with said stop means, extending through said housing into said body portion; means associated with said rotatable member for positioning said body portion with respect to said rotatable member in a xed spatial relationship wherein said contact arm is held in rotatable contact with said electrical contact; a shaft extending into said housing; and means coupling said rotatable member to said shaft for rotation .therewith and for limited longitudinal movement with respect thereto.

4. A rotary switch comprising: a housing; a body portion, including an index plate, a front spacer, a stator having electrical contacts and a rear spacer confined in that order within said housing; means for holding said plate, front spacer, stator, and rear spacer in a fixed relationship; a rotatable member, having a contact arm and indexing means extending through said housing into said body portion; and means associated with said rotatable member for positioning said body portion with respect to said rotatable member in a fixed spatial relationship wherein said contact arm is held in rotatable contact with said electrical contacts and wherein said index means is operably associated with said index plate.

5. The rotary switch of claim 4 wherein said index means includes a pair of balls held in an aperture within said rotatable member and urged against the index plate by an index spring.

6. A rotary switch comprising: a housing having a front cover and a rear cover joined in sealed relationship, said front cover having an aperture formed therein; a bushing in sealed relationship in said aperture and having a stop member extending into said housing; a shaft extending through said bushing and having a portion thereof operably associated with said stop member for limiting the rotation thereof; a rotor, having a contact arm; means coupling said rotor to said shaft for rotation therewith and for limited longitudinal movement with respect thereto; a body portion, including a stator having electrical contacts, held in said housing; and means associated with said rotor for positioning said body portion with respect to said rotor in a xed spatial relationship wherein said contact arm is held in rotatable contact with said electrical contacts.

7. The rotary switch of claim 6 wherein a seal ring is mounted on said shaft for sealing said switch.

8. The rotary switch of claim 6 wherein a plurality of wires are electrically connected to said electrical contacts and extend through said rear cover.

9. The rotary switch of claim 6 wherein a rotor plug is tixedly engaged with said rotor for maintaining said fixed spatial relationship.

1t). In a rotor for a rotary switch, a cylindrical body portion having rst and second end faces and having a longitudinal axis; a pair of intersecting ridges formed on said rst face for coupling to a driving shaft; a conically shaped extension formed on said second face; a pair of intersecting slots extending though said conical portion into said body portion; and a groove formed about said conical section for engaging with a stator.

11. The rotor of claim 10 including a rotor plug adapted to be inserted into said pair of slots for maintaining a stator in said groove.

12. The rotor of claim 11 wherein locking projections are provided in saidy intersecting slots `and said rotor plug for maintaining said plugin a iixed position with respect to said rotor.

13. The rotor of claim '11D wherein a contact spring is maintained in said 'intersecting slots.

14. A rotary switch comprising: a rotor having a longitudinal axis and rst and second ends; a Vcontact arm; means formed in said rst end for containing said arm and for holding said arm at a substantially fixed longitiudinal position on `said rotor rotating means; means formed in said second end for coupling said rotor to a rotating means; said stator having a central aperture and arcuately arranged electrical contacts; and means formed on said rst end for positioning said rotor with respect to said aperture so that said arm contacts said electrical contacts. Y

15. A multiplesection rotary switch comprising; a plurality of rotors, having individual contact arms, arranged along a longitudinal axis wherein adjacent rotors arercoupled together; a plurality of stators, individually having central apertures, each stator having at least one stator contact; means confining each individual rotor within the aperture'of one of said stators; means loosely connecting said rotors tor automatically adjusting the coupling between adjacent rotors to maintain said arms in contactV switch; at least one tie rod extending longitudinally along said switch sections and having a bent end portion embracing the outer switch section at one end of said switch; and spring means integral with the other end of said tie rod and enaging the outer switch section at the other end of said switch to urge said switch sections toward each other. Y

V18. A rotary switch comprising: a housing including a front housing member having an open front end; a stator in said housing and having a plurality of contacts; a rotor rotatably mounted relative to said stator and having at least one contact movable into and out of engagement with said stator contacts; a shaft coupled to said rotor for rotation thereof and extending outwardly of said housing open end; a bushing in said housing open end and rotatably supporting said shaft; means providing a seal between said housing and said bushing; means providing a seal between said shaft and said bushing; and a rearv housing member sealingly engaging the rear end of` said front housing member.

, 19. A rotary switch comprising: a stator having spaced contacts; a rotor rotatably mounted insaid stator .andV y carrying at least one contact; a shaft; means supporting said shaft for rotation relative to said stator; and means coupling said rotor to said shaft for rotation therewith S and` for limited longitudinal movementY with respect thereto. Y'

20. A multiple section rotary switch comprising: a plurality of axially aligned rotors, each' rotor having an extension at one end thereof and arecess at the other end thereof, adjacent rotors being coupled for rotation together by the intertting ofa rotor extension in an adjacent rotor recess; a rotor contact mounted in each rotor recess; a circumferential groove extending around each rotor; a stator mounted in each groove and having spaced stator contacts, each said stator being positioned in abutting relation with one of said rotor contacts, whereby upon rotation of said rotors, said rotor contacts are moved into androut of engagement wtih the contacts on the abutting stator to effect the switching action; and at least one longitudinally extending tie rod passing through each of said stators lto lock said stators against rotation.

21. A multiple section rotary switch comprising: a plurality of axially aligned rotors,`each rotor having an extension at one end thereof and a recess at the other end thereof, adjacent rotors being coupled for rotation together by the interfitting of a rotor extension in an Aadjacent rotor recess; a rotor contact mounted in each rotor recess; a circumferential groove extending around Y each rotor; a stator mounted in each groove and having spaced stator contacts, Veach said stator being positioned in abutting relation with one of saidrrotor contacts, whereby upon rotation of said rotors, said rotor contacts are moved into and out of engagement with the contacts on the abutting stator to effect the switching action; insulating spacers'between adjacent stators to define with said stators a stator assembly, at least one row of aligned notches in each of said stators and said spacers; and a tie rod extending through said row of notches and having a bent end portion embracing one end of said stator assembly, and a spring clip at the other end of said tie rod and'engaging the other end of said stator assembly.

References Cited by the Examiner VUNITED STATES PATENTS 283,940 8/83 Wheeler 64-8 '2,165,200 7/39 Batcheller 200-155 X 2,201,881 5/40 Bryant et al. 2,263,754 ll/4l Batcheller 200-4 2,303,693 12/42 Hill 20G-16 X 2,3 31,040V 10/ 43 Naster 200-6 2,447,718 8/48 Simpson ZOO-155 X l2,460,216 y6/49 Dalton 64-8 2,525,993 10/50 Youngbeck et al 338-132 2,553,478 5/51 Schleicher 200-6 X 2,576,836 11/51 Hilsinger 200-6 X 2,676,226 4/54 Mucher 338-131 2,781,424 2/57V Woolf 200-6 X .2,817,721 12/ 57 Edwards 200-6 2,971,174 2/61 Lyon. Y 2,980,770 4/61 Nabstedt 200-11 3,094,592 6/63 Fisher 200-6 3,142,187 7/64 Kaneet al. ZOO-'16 X BERNARD A. GILI-IEANY, Primary Examiner. 

1. A ROTARY SWITCH COMPRISING: A HOUSING; A BODY PORTION, INCLUDING A STATOR HAVING ELECTRICAL CONTACTS, HELD IN SAID HOUSING; A ROTATABLE MEMBER, HAVING A CONTACT ARM, EXTENDING THROUGH SAID HOUSING INTO SAID BODY PORTION; MEANS ASSOCIATED WITH SAID ROTATABLE MEMBER FOR POSITIONING SAID BODY PORTION WITH RESPECT TO SAID ROTATABLE MEMBER IN A FIXED SPATIAL RELATIONSHIP WHEREIN SAID CONTACT ARM IS HEALD IN ROTATABLE CONTACT WITH SAID ELECTRICAL CONTACTS; A SHAFT EXTENDING INTO SAID HOUSING; AND MEANS COUPLING SAID ROTATABLE MEMBER TO SAID SHAFT FOR ROTATION THEREWITH SAID FOR LIMITED LONGITUDINAL MOVEMENT WITH RESPECT THERETO. 